At certain frequencies in the far infrared range, coherent radiation may be generated, for example, by molecular lasers which are pumped by Co2 lasers. Many of the frequencies and wavelengths of importance to the spectroscopy of molecules and solid bodies may be within the wavelength range extending from 3 mm to 30 μm (from 100 gigahertz to 10 terahertz). The use of a microradiation source, which may be tunable within the wavelength range and implemented on a semiconductor chip of a wafer for this range of terahertz radiation and which exhibits sufficient power output within the range of between 1 μW and 1 W, may be substantially significant from a technical standpoint for spectroscopic applications in all areas of environmental protection, analytics, and in material characterization in medicine and biology, as well as in chemistry and physics. Another way to generate coherent radiation in the far infrared range is based on the so-called Smith Purcell effect. It provides for generating radiation similar to the method known from the “free electron laser”. Macroscopic electron sources and diffraction gratings having a 100 to 300 μm period may be used to generate a coherent radiation field of polarized radiation having up to 1 μW power.
The reference “Intensity of Smith-Purcell Radiation in the Relativistic Regime”, J. Walsh, K. Woods, S. Yeager, Department of Physics and Astronomy, Dartmouth College, Hanover, N.H. 03755, U.S., pages 277-279, discusses the theory of such Smith-Purcell radiation sources and, additionally, gives experimental results. The reference “A New Source of THz-FIR Radiation” in LEOS NEWSLETTER, February, 1999 by J. E. Walsh, J. H. Brownell, J. C. Swartz, Department of Physics and Astronomy, Dartmouth College, Hanover, N.H. 03755-3528 and M. F. Kimmitt, Department of Physics, Essex University, Colchester, UK, Jan. 7, 1999, pages 11-14, discusses the design and mode of operation of a radiation source in the terahertz region. It may be that these terahertz radiation sources are perfectly efficient, but they do not yet suffice for many analytical applications, and they are not yet miniaturized to a sufficient degree.